Ion beam implanters are widely used in the process of doping semiconductor wafers. An ion beam implanter generates an ion beam comprised of desired species of positively charged ions. The ion beam impinges upon an exposed surface of a work piece such as a semiconductor wafer, substrate or flat panel, thereby “doping” or implanting the work piece surface with desired ions. Many ion implanters utilize serial implantation wherein one relatively large work piece is positioned on a work piece support in an evacuated implantation chamber or end station and implanted or “doped” with desired ions. After implantation is completed, the work piece is removed from the work piece support and another work piece is positioned on the support.
An ion implantation chamber of an ion beam implanter is maintained at reduced pressure. Subsequent to acceleration along a beam line, the ions in the beam enter the implantation chamber and strike the work piece. In order to position work pieces for implantation by the ion beam within the ion implantation chamber, a work piece transfer system is necessary. Work pieces ready for processing are stored in a storage device or buffer. The work piece transfer system includes a first robot system to move the work pieces from a storage device into a load lock system. The first robot system, which is at atmospheric pressure (“in-air”), includes two robotic arms. A first robotic arm moves work pieces from the storage device to an aligner, where the work piece is rotated to a particular crystal orientation. A second robotic arm moves the aligned work piece from the aligner to the load lock system.
The load lock system is in communication with the evacuated implantation chamber and includes one or more load locks for receiving a work piece. The load locks can be selectively evacuated. When a work piece is positioned in a load lock by the second robotic arm, the load lock is closed and pumped down to a reduced pressure. After the load lock is reduced to a suitable pressure, a sliding door on the load lock is opened so that the work piece is made available for transfer into the implantation chamber interior region.
In prior art ion implanters, the work piece transfer system further included a second robot system located within the evacuated implantation chamber (“in-vacuum”) for moving a work piece from the load lock to the work piece support, where the work piece was positioned for implantation. After implantation of the work piece, the second robot system removed the implanted work piece from the work piece support and return to the load lock. The first in-air robot system then moves the implanted work piece from the load lock to a storage device. U.S. Pat. No. 5,486,080 to Sieradzki concerns a system for high speed movement of work pieces in vacuum processing. The system employs two wafer transport robots for moving wafers from two load locks past a processing station. Additional patents relating to serial implantation end stations are U.S. Pat. Nos. 6,350,097, 6,555,825, and 5,003,183.
While work piece transfer systems including a second in vacuum robot system disposed within the implantation chamber are workable, it would be highly desirable to simplify the work piece transfer system by eliminating the second in-vacuum robot system. The in-vacuum robot system is both costly and complex and, by virtue of the fact that it is located within the implantation chamber, requires space within the evacuated implantation chamber. Since the implantation chamber requires a pumping system for maintaining the chamber interior region in a reduced pressure state, it is desirable to minimize, to the extent possible, the size of the chamber interior region. Further, smaller chambers are desirable in that they require less clean room space.
The present invention is directed to a work piece transfer system for an ion beam implanter that eliminates the need for an in-vacuum robot transfer system disposed within an evacuated implantation chamber of the implanter.